Pyramidal or conical shaped tamper heads and method of use for making rammed aggregate piers

Abstract

A tamper head having an elongated pyramidal or conical shape is used to construct rammed aggregate piers. The pyramidal or conical shape of the tamper head is more efficient at building up lateral earth pressure and provides for greater economy in the construction of the piers than available with existing methods that rely on tamper heads with flat bottoms and beveled sides.

1. A method of constructing aggregate piers comprising the steps of:
 forming an elongated cavity in a ground surface, said cavity having a sidewall and a generally uniform cross-sectional area; 
 placing a lift of aggregate into the cavity with a lift thickness approximately equal to a distance across the cavity; 
 tamping the lift with a pyramidal or conically shaped tamper head having a substantially hollow portion and a top or base approximately equal to said cross-sectional area of the cavity, and a bottom or tip no more than about 20% of the area of the top or base, to increase the lateral stresses in the sidewall of the cavity, wherein the tamper head is sized and configured to connect to and be manipulated by a tamper rod, mandrel or shaft that connects to and communicates a mechanized force from a power source to the tamper head for delivery to the lift of aggregate; and 
 repeating the placing and tamping steps with successive lifts. 
 
     
     
       2. The method of  claim 1  wherein the step of tamping includes using a tamper head having an inclination that varies from about 45 degrees to about 75 degrees from horizontal. 
     
     
       3. The method of  claim 1  wherein the step of tamping includes using a tamper head that has a conical shape. 
     
     
       4. The method of  claim 3 , wherein the step of tamping includes using a tamping head that has a truncated conical shape. 
     
     
       5. The method of  claim 1  wherein the step of tamping includes using a tamper head that has a pyramidal shape. 
     
     
       6. The method of  claim 5 , wherein the step of tamping includes using a tamping head that has a truncated pyramidal shape. 
     
     
       7. The method of  claim 1  wherein the elongated cavity is generally cylindrical and the step of tamping includes using a tamper head having a top cross-wise dimension approximately equal to a diameter of the cavity. 
     
     
       8. The method of  claim 7  wherein said tamper head top dimension is no less than about 90% and no more than about 110% of the diameter of the cavity. 
     
     
       9. The method of  claim 1  wherein the step of placing a lift of aggregate includes using aggregate having at least one of stone with fine materials, recycled concrete, recycled asphalt, slag, and cement treated base. 
     
     
       10. The method of  claim 1  wherein the step of forming the cavity is by drilling. 
     
     
       11. The method of  claim 1  wherein the step of forming the cavity is by penetrating and extracting an elongated tube or mandrel. 
     
     
       12. The method of  claim 11 , wherein the step of forming the cavity is by penetrating and extracting a tapered and elongated tube or mandrel. 
     
     
       13. The method of  claim 1  wherein the step of tamping includes using a tamper head having a generally pointed bottom or tip and having a circular confinement plate attached to said tamper rod, mandrel, or shaft. 
     
     
       14. The method of  claim 1 , wherein the step of tamping provides stress build-up including more than 50% lateral stresses in the sidewall of the cavity. 
     
     
       15. An apparatus for forming an aggregate pier in a generally vertical cavity in a ground surface, said cavity having a generally circular cross-section, said apparatus comprising:
 a power source configured to generate a mechanized force; 
 a tamper rod, mandrel or shaft in force communication with said power source and configured to move in response to the mechanized force; and 
 a tamper head comprising a generally pyramidal or conical body tapering toward a point at its lower end and having a cross-section at its upper end which is at least about 90% of said cavity cross-section, said tamper head including a substantially hollow portion and being configured and sized to attach to and be manipulated by the tamper rod, mandrell or shaft, wherein said tamper head receives and delivers the mechanized force from said tamper rod, mandrel or shaft. 
 
     
     
       16. The apparatus of  claim 15 , further comprising a circular confinement plate mounted at an upper end of said pyramidal or conical body, said confinement plate having a diameter substantially equal to or greater than a longest dimension of an upper end of said pyramidal or conical body. 
     
     
       17. The apparatus of  claim 16 , wherein the confinement plate is attached to said tamper rod, mandrel, or shaft. 
     
     
       18. The apparatus of  claim 15  wherein said lower end is blunted, and has a blunted area no more than about 20% of an area of the upper end. 
     
     
       19. The apparatus of  claim 15 , wherein said upper end of the generally pyramidal or conical body has a greatest dimension equal to between about 90% and about 110% of a diameter of said cavity. 
     
     
       20. The apparatus of  claim 15 , wherein said generally pyramidal or conical body tapers at an angle to horizontal of about 45 degrees to about 75 degrees. 
     
     
       21. The apparatus of  claim 20 , wherein said generally pyramidal or conical body tapers at an angle to horizontal of about 60 degrees. 
     
     
       22. The apparatus of  claim 15  wherein the body has a conical shape. 
     
     
       23. The apparatus of  claim 22 , wherein said body has a truncated conical shape. 
     
     
       24. The apparatus of  claim 15  wherein the body has a pyramidal shape. 
     
     
       25. The apparatus of  claim 24  wherein said pyramidal shape is hexagonal in cross-section. 
     
     
       26. The apparatus of  claim 24  wherein said pyramidal shape is octagonal in cross-section. 
     
     
       27. The apparatus of  claim 24 , wherein said body has a truncated pyramidal shape. 
     
     
       28. The apparatus of  claim 15  wherein the tamper head upper end has a diameter approximately equal to a diameter of the cavity. 
     
     
       29. The apparatus of  claim 15 , wherein said tamper head upper end has a greatest dimension equal to between about 90% and about 110% of a diameter of said cavity. 
     
     
       30. A tamper head for forming an aggregate pier in a generally vertical cavity in a ground surface, said cavity having a generally circular cross-section, said tamper head comprising a generally pyramidal or conical body tapering toward a point at its lower end no more than about 20% of a cross-section of an upper end of the body, said upper end cross-section being at least about 90% of said cavity cross-section, said tamper head including a substantially hollow portion and being configured to attach to a tamper rod, mandrel or shaft that communicates a mechanized force from a power source to the tamper head, and wherein the tamper head is sized to be manipulated by said tamper rod, mandrel or shaft.